1. You can create any link through the Joomla menu system. To do this you'll have to find the url of the account page, I don't think it is unique per customer in Virtuemart. Then in Joomla create a link-url to that page. To remove the link from Virtuemart you would have to edit their shop module but I do not know what file or where you would remove it from. Their forums at www.virtuemart.net
might be able to help you on that one.
2. The My Account section is all controlled by the login in module in Joomla. In the login module manager you have an option to redirect the user once they login. Just put the url of the account page in the login redirection box and it will take your customers to the account screen on login.